Test-circuit for multiple switch-boards



C. E. SCRIBNER. TEST CIRCUIT .FCR MULTIPLE SWITCH BOARDS. K

Patented Jan. 26, 1892.

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M www MM] 7 C@ UNITED STATES CHARLES E. SCRIBNER,

PATENT OEEICE.

OF CHICAGO, ILLINOIS.

TEST-CIRCUIT FOR MULTIPLE SWITCH-BOARDS.

SPECIFICATION forming part of Letters Patent N0. 467,901, dated January 26, 1892.

Application tiled May 29, 1891.

To all whom it may concern:

Be it known that I, CHARLES E. SCRIBNER, a citizen of the United States, residing at Chicago, in the county of Cook and State of Illinois, have invented a certain new and useful Improvement in Testing Systems for Multiple SwitclrBoards, (Case No. 259,) of which the following is a full, clear, concise, and exact description, reference being had to the accompanying drawings, forming a part of this specification.

My invention relates to testing apparatus for multiple switch-boards of telephone-exchange systems. Its object is to provide an audible test-signal of a character distinct and different from any sound which may be produced by extraneous and accidental causes.

In the system of multiple switch-boards in most general use the operation of testing at one multiple switch board to determine whether any line isin use at some other board is accomplished in the following manner: fhen a connection is made to any line at any board, an earth connection is completed through a battery to the test-ring or frame of the springjack at which the connection is made. The frames of all the spring-jacks belonging to one line are in electrical connec tion and in the metalliecircuit system are connected to one side of the line. If now a connection be made from the test-ring of a spring-jack at another board through a tele` phone to earth, the battery-circuit willbe completed, and at each test a click will be heard in the telephone. The circuit directly involved in this process ot' testing-those portions of the switch-board connections which are necessary to complete the circuit of the test-current in a busy line-is commonly designated as the test-circuit. When, however, the telephone-lines extend parallel or in proximity to electric-railway lines or other conductors carrying heavy and varying currents, currents and electrostatic charges varying in character according to their causes are induced upon the telephone-lines, and when an earth connection is made to the line, as through a testing-telephone, a false signal is produced in the telephone, leaving it uncertain whether the line tested is in use or not, and thus causing confusion.

Serial No. 394,498. (No model.)

My invention herein described is designed to obviate this diiculty. The test-signal is so produced that it could not be counterfeited by any sta-tic discharge or induced current through the telephone. I include in the connection between the test-ring and earth a dynamo giving a pulsating current of constant direction and of such period as to produce no sound in a telephone included in its circuit, each pulsation having a duration equal to one-halt` of the period, and included in the circuit from the telephone to earth is a second dynamo, giving pulsations whose period and duration are the same as those of the rst dynamo,but whose direction is opposite with reference to the test-circuit, and which lag one hundred and eighty degrees behind the pulsations of the first dynamo, and a polar ized device adapted to make an audible signal when its armature vibrates. When a pulsating or continuous current of constant direction traverses the polarized device, it gives no sound; but when itis traversed by the composite current from the two d ynamos, which is, in fact, an alternating current, it is thrown into vib1ation,which may be rendered audible. Thus when the line tested is not in use no test-signal is given; but when the line is in use a signal which is reliable and certain is produced. I shall have occasion to refer to the action of these two currents hereinafter, and I find it convenient to designate those pulsations or intermittent currents from one dynamo which are in a-phase lagging one hundred and eighty degrees or onehalf period behind those of the other dynamo, so as to occupy in the resultant or composite current the intervals between the currents from the first dynamo as complementary currents.

I have devised several forms of polarized vresponsive devices adapted to my invention,

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telephone is rapidly made and broken, and a succession of clicks is heard in the telephone. This method I find preferable.

My invention will be more readily understood by reference to the accompanying drawings, Figures l, 2, 3, and 4, which are illustrative thereof.

In Fig. l I have shown three subscribers stations connected, as usual, to their respective sprin g-jacks and calling apparatus on two sections of multiple switch-board. I have shown at each of the switch-boards an operators listenin g-key, telephone-set, connecting'- plugs, and testing apparatus, and at the second board the operators calling-keys. These calling-keys and their operation are too well known to need description. Fig. 2 is a graphic representation of the character of the current from one of the dynamos in a manner well understood by those skilled in the art to which my invention pertains. Fig. 3 is a similar representation of the character of t-he current from the other dynamo. Fig. 4 represents in the same manner the composite current of both dynamos in series.

Having thus generally described my invention, I will now proceed to describe it and its operation in greater detail.

Parts in the drawings will be indicated by letters and figures of reference, similar parts being designated by similar letters and figures of reference.

Reverting to Fig. l, l, 2, and 3 are three subscribers stations connected to the exchange. Line from station l, Jfor example, may be traced by line ct through the linespring and back contact of spring-jack a at the first board at the left of the drawing, thence similarly through spring-jack d2 at the second board, thence the circuit would be normally through annunciator CL3, and thence returning by line d4 to station l. The returnwire a4 is connected to the frames of the spring-jacks a a2, and an answering-jack d5 is bridged in between the lines d and a4. Circuit from station 2, which is represented as a grounded line, may likewise be ,traced through line b, jacks b b2, annunciator b2,

answering-jack b5, andY return-line b4, resist-n ance h6, and earth to station 2. Circuit from station 3 may be traced through jacks c c2. The answering-jack and calling annunciator are not shown.

I have shown stations l and 2 connected together for conversation at the second board by means of the flexible cord and terminall connected lines; but this key is shown in its open position, whereby the telephone is disconnected from the lines. Connected to the sleeve-strand-of the cord joining the connecting-plugs CZ d. I have shown one of the dynamos described N. Two pole-pieces N S furnish an approximately uniform magnetic field, in which revolves armature O, shown in the drawings as of one turn of wire. One end of the armature is connected to a contact bearing against a brush p, which is grounded. The other terminal is connected to a commutator-segment q, which during one-half of each revolution bears against brush p', which is connected to the sleeve-strand ofA the connecting-cords. An idle segment is provided upon the commutator in such position that it short-circuits the brushes during that half of the revolution in which the brush p is not in contact with segment q.

The character of the current is graphically represented in Fig. 2. Beginning with the point o a current flows which gradually increases from O at r to a maximumv at r after a quarter of a revolution orninety degrees. In the next quarter-revolution the current falls again to O at r2. During the whole ot' the succeeding half-revolution to r2 no current flows. The armature-circuit is open and the brushes are short-circuited. Thus a pulsatory current, or, if no test-circuit is completed, an intermittent electro-motive force, is closed to the sleeves of the connecting-plugs (Z CZ', and henceto the test-rings of the lines between which a `connection is made by means of them. I have shown a retardation-coil tincluded in circuitrbetween the sleeve-strand and the brush p of the dynamo, in order that another or several more connections may be extended from the same dynamo to other'pairs IOO ot' plugs at the same or at other boards withl out appreciably crossing the lines together. The operators outfit at the rst board is similar to that at the second. At this board I have shown the operators outfit as in the act of testing the spring-jack c of line 3. The listening-key L is in position to connect the telephone-set M tothe connecting-strands of the plugscZ2 d3. The telephone-circuit may be traced from the tip of plug CZ2 through the corresponding cord-strand, through spring Z2, contact Z2, through telephone-set M', returning to contact Z5, spring Z4, through the other strand of the cord to the sleeve of plug CZ2. The circuit may also be traced from tip of plug CZS, through its connecting-cord, through condenser G to spring Z2, and through the telephone back to spring Z5, and thence to the sleeve of plug (Z2. Hence it is evident that the telephone-set M is in a shunt or bridge connection between the sleeves and tips of the two plugs.

The two terminals of the telephone-coil are connected, as traced, to the springs Z2 Z5; but to the center of the coil a connection is made which extends through another dynamo N2 similar to that just described. The period or IIC rate of the pulsations of this dynamo is exactly the same as that of the other; but the com inutator is so disposed that the pulsations of this dynamo lag one hundred and eighty degrees behind those of N', and are ot opposite phase or direction. The character of the current from this dynamo is shown in Fig. 3. It Will be seen that the periods of activity of N coincide with the periods of idleness of N2 and the periods of idleness of N With those otl N2s activity. At the second board at the right I have represented a dynamo N3 bya circle similar to dynamo N2 at the first board.

Included in the telephone-circuit between the tip of test-plug d2 and the telephone is the coil of a polarized relay u, Whose contacts key L in its alternate position, whereby she is placed in communication with station I. Having ascertained with what line a connection was desired-saywith station No. c7-her next operation would be to test that line to determine whether it Was in use at some other board or not; but this test I will for the present ignore, and will consider it at lengthl later. The operator thrusts her second connecting-plug d into jack b of line to station 2. The circuit from station l is now extended from the line-spring a2, through the tip of plug d, condenser G, tip of. plug d', line-spring h to station 2, thence returning by the path previously traced to frame of jack b', sleeve of plug d', sleeve of plug d to frame of jack a2. Having thus made the desired connection, the operator sends a call-signal to station 2 by means of the callin g-keys, anda calling-generator throws listening-key L into the position shown and leaves stations l and 2 in communication. Dynamo N is now impressing an intermittent electro-motive force, as represented in Fig. 2, upon the test-rings of both lines a4 and h4, which results in the case of the latter line in a slight current th rough drop a2 over line l), through subscribers station 2 to earth; but the strength of the current is so slight as not to operate drop CL3. Since its direction is constant, it will not ring the bell at station 2. Moreover, the period of pulsation is so slow that the separate pulsations do not blend into amusical tone. I iind that Iitteen pulsations per second may be sent through a telephone Without producing a tone, and when the fluctuation of the current is gradual, as represented in Fig. 4, as is the case With an armature revolving in a uniform magnetic held, the attraction and release of the diaphragm of a telephone in circuit is so gradual as to produce no sound Whatever.

Care must be takenyhowever, to insure that the brush p reaches and leaves the commutator-segment when the electro-motive force of the armature is at exactly zero, asat points fr r2 in Fig. al., else there would be an abrupte starting or cessation of a current through the circuit-,which would produce a click in the telephone. Suppose, now, that the operator at the irst board has occasion to test jack a' ot line from station I to determine Whether or not the line is already in use at another board. She places the tip of her testing-plug d2 against the f rame or test-rin g of jack a. The circuit from brush p of dynamo I will now be completed through the retardation-coil, through the strand of cord to sleeve of plug d, to test-ring of jack a2, thence to test-ring of jack a', to tip of plug d2, cord, spring Z3, and contact Z2 of her listening-key L', through the coil of the polarized relay u, through one-halt of the coil of telephone M', through the brushes 1T p3 of dynamo N2 to ground, thence returning to dynamo N. Let thc coinmutator segments ot dynamo N be in position to allowa current to iow from the armature, then the cornmutator of dynamo N2 is at the same 1nstant in a position to short-circuitits brushes p2 p2, and a current flows from dynamo- I\ through the circuit traced in one direction, throwing the armature ot polarized relay u to one side and closing the shunt around the telephone, and so producing a click in the telephone. Onehalf-revolutionlaterthecommutator ot dynamo N has short-circulted brushes p p', while that of dynamo N2 is allowing a current to tiow in the opposite direction through the same circut. The polarized armature ot relay u is thrown to the other side, opening the shunt around telephone M and producing another click. Thus a composite alternating current, (represented 1n Fig. 4,) made up of the pulsatory currents of the two dynamos, will fiowin the test-circuit, and through the agency of the polarized relay Will produce a rapid succession of sharp clicks in the testing-operatoi"s telephone, which will be indicative to her that the line tested is busy.. Suppose, however, that the operator test the jack c of the line from station 3, which is at present not in use. The line connecting station 3 with the telephoneexchange is shown as metallic and is nowhere connected to ground; but if it were a grounded line, as that from station 2, a slight pulsating current Would obviously find circuit through the various grounds of the line; but this current, being constant in d1- rection, would produce only one click in the telephone, or, if the relay Were in the correspondin g position, no click, since the tendency ot the current through the relay-coils would be to retain the armature in one position.

It will be noted here that it is necessaryto have the polarized relay so arranged with reference to the direction of this current from dynamo N2 that it shall separate its contacts,

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and thus open the shunt around the telephone. i

It Will be understood that the brushes 192133 of dynamo N2 are to be adjusted in the same manner as those of dynamo N', Vin order not to disturb the proper Workin g of telephone M.

I have sometimes placed a switch in circuit with telephone M so arranged that the dynamo N2 could he included in circuit only when a test was about to be made; but with a proper adjustment of the various apparatus I do not find this necessary.

It is obvious that my invention might be applied with little or no alteration to any of the Well-known forms of test-circuit for multiple switch-board. Hence I do not limit myself to the precise arrangement ot circuits shown.

Having thus fully described my invention, I claim as new and desire to secure hy Letters Patent-V 1. The combination, in a circuit open at two points, of contacts whereby the circuit may be closed at either point or at both of two sources of intermittent currents, one source giving currents of opposite direction to and complementary to those from the other source, and a polarized device adapted to respond to composite currents from the two sources, in the manner and for the purpose specified.

2. In a testing-circuit for multiple switchboards, thecolnbination of spring-jacks having test-rings electrically connected together, an earth connection including a retardationcoil and a source of intermittent currents of electricity, a testing-plug adapted to be brought into contact With one of the testrings and having included bet-Ween it and the earthY a second source of intermittent currents opposite in direction and complementary to those from the first source, and a polarized device adapted to respond audibly lo the composite current from. the-two sources, in the manner and for the purpose specified.

3. The combination, With telephone-lines extending through spring-jacks having testsource of in termittent current, a second source of intermittent current Whose pulsations are of the same frequency as those of the first source, out opposite in direction in' the circuit to and complementary to' those from the i first source, a polarized responsive4 device included in the circuit adapted not to respond to currents kof constant direction, but to respond to the composite current from both sources, and a conductor or conductors adapted to complete the electric circuit, in the manner and i'or the purpose specified.

5. In combination, in an. electric circuit, a source-ot intermittent current, asecond source of intermittent current Whose pulsations are `ot` the same frequency as those of the rst source, but opposite in direction in the circuit to and complementary to those from the rst source, a polarized relay having its magnet-coil included in the circuit and its relaycontacts adapted when closed to close a shuntcircuit around a telephone-coil normally ineluded in the circuit, andV a conductor or conductors adapted: to complete the electrical circuit, as and for the purpose described.

In Witn ess whereof I hereun tosubscribe my name this 27th day of April, A. D. 1891..

CHARLES E. SCRIBNER.

Vitnesses:

ELLA EDLER, FRANK R. MCBERTY. 

